Apparatus adapted to duplex telephony over a single carrier frequency



PL TATz Dec. 20, 1932.

APPARATUS ADAPTED TO DUPLEX TELEPHONY OVER A SINGLE CARRIER FREQUENCY Filed July 11, 1929 INVENTOR PAUL T TZ ATTORNEY Patented Dec. 20, 1932 UNITED STATES PATENT o Fica- PAUL TKTZ, OI BERLIN, GERMANY, ASSIGNOB TO TELEFUNKEN GESELLSOHAI'I. FUR

' DRAHTLOSE TELEGBAPHIE M. B. H, BERLIN, G'IILRMAINY- arrannros finer-ran TO DUPLEX TELEPHONY OVER A. snieLE cnnnmn FREQUENCY Application filed July 11, 1929, Serial No. 377,390, and in Germany May 4, 1928.

Application for this invention filed iin Germany May 4, 1928.

The present invention relates to a system of radio frequency telephony, especially along wire lines, in both directions on one and the same carrier wave.

An object of the invention is to prevent undesirable regenerative actions such as might be due to thereaction of the transmitter upon the receiver apparatus;

- According to the present invention this object is accomplished by suppressing the carrier wave by well known means in one direction of transmission such as, say, from the called to the calling apparatus, so that there may be obtained higher amplification in the called apparatus. Beyond that, recourse may be had in operation to the suppression of one side band, so that in one direction of traflic or communication only one side band,

say, the upper one, and in the other or 011-- posite direction, the respective other side band, say, the-lower one .in this instance, is

used for the transmission of speech.

In the direction from the calling tothe called apparatus, the suppression of the carrier wave, as a matter of principle, is dispensed with inasmuch as the calling or ringing apparatus takes care of the supply of radio frequency (carrier frequency) for side band production in the called apparatus, and because the carrier current is to be made available for the solution of certaimringing problems or functions such as for connecting the apparatus with ordinary automatic telephone centrals.

The suppression of the carrier wave in radio frequency telephony, per se, is well known and has been described'heretofore. As a general rule, in these arrangements disclosed in the prior art, a distinct auxiliarygenerator is provided at the receiving oflice for the carrier frequency suppressed in. the transmission, in order to restore with the ensuing radio frequency band'beats of acoustic frequencies. In this connection, however, great care is to be taken in order that the frequency of this auxiliary generator will agree as closely as possible with the suppressed carrier wave frequency lest the voice'be unduly distorted. In contrast thereto, however, the idea of suppressing the carrier frequency in sys terms of the type which include a joint carrier-wave generator for thetwo inter-communicating oflices offers the special advantage that the suppressed frequency is restorable fact that the relays are denoted by capital letters while the contacts, operated by said relays are denoted by corresponding small letters, thus, relay B operates contacts 6 6 Every telephone equipment has two voice outlets, one audio frequency 1, 2 and one radio frequency 4;, 2, see Fig. 1. Theseconnectlng lines are united with the transmitter modulating outfit 18 and the receiver demodulating outfit 19 in known manner by way of dif-' ferential connections or circuit arrangements whose chief constituents are: difi'erential transformers 12 and 36, respectively, art ificial balancing lines (simulations) 14 and 37 (the latter being balanced for all frequencies under consideration) and call blocking condensers possibly required on the audio frequency end, 4, 4 and simulation (balancing li es) 13, 13. It is further advisable for the output end of the modulator and the input end of the demodulator to provide su table filter means 35 and 25, respectively which are arranged so as to be changed over in dependence upon the direction of callmg 1n such a way that at the ofiice or equipment which is calling, filter 35 allows the transmission or passage of the carrier wave and only one side band, and filter 25 only the-pas sage of the respective other side band, whereas, at the called station, filter 35 will pass only one side band, and filter 25 the carrier frequency and the respective other side band.

The fact that the filters may be reversed is indicated by condensers 26 and 49, and condensers 33 and 60 respectively, and the double-throw switches d, and d respectively.

Between the audio frequency line '1 and 2 and the transmitter modulator 18, it is preferable to insert a further filter 17 passing only a band that is absolutely required for speech or voice transmission, let us ,say, a filter having a band width of from 200 to 2500 cycles, and also in the audio frequency connection to the receiver a similar filter chain 16 could be inserted whereby the differential balance at the audio frequency end is facilitated, while at the same time undesiredback-feeding between the transmitter and receiver outfits combined both on the radio frequency and audio frequency ends is precluded. The radio frequency line 42, 42 consisting, for instance, of a high-potential transmission line, is united with differential means 36, 37 by way of condensers 41 (say, high-potential condensers) by means of a transformer 40, the coupling between the radio frequency line and the receiver being adjustable by the aid of variable condenser 39. 88 denotes aninductance coil required for tuning. I

The modulator and the demodulator are merely indicated schematically in the drawing. They are wellknowninthe art, and it is furthermore quite immaterial here how many vacuum tubes they comprise, and what particular connecting scheme is resorted to. Also the means for suppressing the carrier wave in the modulator are Well known, in-

deed, it may suffice here to cite one of the many conceivable arrangements which probably would be used by preference and which 1s shown in Fig. 2. i

In this scheme the carrier wave of an oscillator 44 is fed by way of a transformer 46 to the grids of two thermonic 'tubes 43, 43 connected in parallel, and is modulated in phase opposition by voice frequencies by way of a transformer 45. The plate currents by means of a differential transformer 47 being as symmetrical as feasible are fed to further clrcuits, say to a filter and thence to an ampl1fier. In the absence of voice modulation, the actions of the two plate currents upon the secondary winding of transformer 47 he neutralized, while during voice transmission, the symmetry of the two tubes is distributed or elimlnated in such a way that only the two side bands will be further transmitted, and of these, if desired, one may be stopped in any well known manner. I

Also the internal arrangement of the thermionic tubes and their circuits in the case of the demodulator is immaterial so far as this invention is concerned. However, what is of utmost importance is to takecare so thatinthe case of fluctuations of line attenuation (or of any transmission relations or conditions at all between remote outfits), the incoming volume will be as uniform as possible, and that in the called apparatus, the transmitter modulator will be furnished from the receiver at all events withv a su'fiiciently constant carrierwave amplitude. The arrangement serving this end usually consists in that, at some suitable point ahead of the input end of the modulator or else in the modulator itself, for instance, in its amplifier circuit, radio fre quency potential is taken off or tapped and fed to a separate regulator means, the latter consisting most suitably of a rectifier and amplifier, and that the rectified and amplified current which can be used as a measure for the amplitude for the radio frequency carrier ivave coming in-from the other apparatus) is employed for the object to correct by convenient electromagnetic means the amplification factor of the receiver, say, by regulation of the biasing potential in any one of the grid circuits of the receiver, or by the Variation of gain regulators or potentiometers disposed in parallel relation to the input or output circuit of the whole receiver or some stages thereof. Inasmuch as the details ofthis regulating device do not form a part of the invention, it may be suflicient to indicate here the said regulator device 20 and its connection with the demodulator in a very general way. Referring to the drawing, it is indicated by the arrow pointing from 19 to 20 at the connecting lines 23 that radio frequency energy derived from anyone of the circuits of the demodulator is fed to the regulator 20, while similarly by the arrow along connecting lines 21 pointing from 20 towards 19 it is indicated that over this way the rectified and amplified regulating current adjusts the amplification factor insome suitable manner.

Apart from the said regulator device 20, there is connected with the demodulator receiver a relay A, most suitably by way of device20, said relay being caused to respond as soon as the receiver receives radio frequency energy from the other apparatus. The said relay controls a working contact a whose function will be explained in what is to follow, while in addition a ringing relay could be employed in such a way that it actuates a suitable signal device upon the call coming in. from the radio frequency apparatus. Said signalling device per se is well known and needs no further explanation and illustration. For instance, it may consist of a signal lamp or alow-frequency alternating current source whose call currents are passed over audio frequency lines 1, 2 to the audio frequency subscriber.

The operation of the system described is'as follows: I

First of all let us assume that it is desired to call another station. Then-in such a case the line loop 1, 2 will be closed in the usual manner by lifting the telephone receiver not shown. When this is done the line relays prevails the radio frequency generator 44 is connected in. the circuit by way of the working contact 65 which has been closed when B was energized, thus, the transmitter'modulator 18 will be supplied with carrier frequency required for communication. This is evident from the drawing since when the contact 6 is closed the generator 44 is connected directly in circuit with the transmitter modulating outfit 18. It is also to be noted that the radio frequency generator 44 is also connected to the receiver demodulator outfit 19 through the contacts (2 and 03 This is necessary because the receiver must be supplied with radio frequency energy in order that it may be combined with the side band received from the called station since as stated before the signals from the called station to the calling station are transmitted only by means of a side band. It is to be distinctly understood that the adding of the carrier wave in the receiver apparatus '19 need not necessarily be accomplished as shown in the drawing. Indeed, in

caseof inexact differential balance the receiver may be supplied by way of the radio frequency outlet 88 from the transmitter modulating outfit 18 in any satisfactory manner. l[f the operation of the transmitter and the receiver is based upon the suppression of one side hand then as above pointed out suit-- able filters 35 and 25 may be employed so that with the make and break contacts (i and (Z in the position shown the transmitter sends out onl the carrier wave and one side band while the receiver 19 receives the side band coming from the other apparatus, that is, from the called station. The operation of these filter devices for suppressing side bands etc. is well known in the art. Suffice it to pay here that any of the well known types may be employed for the purposes desired.

The operation of thesystem when a call is initiated from a similar circuit elsewhere and is to be received in the circuit shown in Figure 1 is as follows: 5

In such a case the relay A upon the receipt of radio frequency is energized thereby closing the contact al This, of course, occurs beforethe relays B, G-become energized by the lifting of the telephone receiver of the station; Thus, with the closing of a relay D is energized by means of the battery 6. This in turn causes the closureof the contact al which may be referred to as a holding contact there: by maintaining the relay D energized. Upon the energization of D the other contacts controlled thereby, namely, d d d, and dfare operated with the result that the radio frequency generator 44 is disconnected from the transmitter modulator 18 and from the receiver demodulator 19. It will be seen, however, that the connections are such that the transmitter modulator 18 will be fed with the requisite carrier frequency from the receiver .19 by way of line 15, 15 and contacts J and (i In order to insure relay D remaining ener- I gized a working contact c, is provided in arallel to the contact a It is evident rom what has preceded that when the telephone receiver is lifted by the person receiving the call the rela s B and C are energized with a result that t e contact 0 is closed thereby a suring a closed path for the energization of D in case contact a should happen to fall off during the conversation as might be the case if the relay current has been adjusted to an. insuliiciently high 'value.

If the filter circuits 35, 25 are used they are changed by the reversal ofcontacts d d so that now the receiver 19 will receive the carrier frequency from the other apparatusin addition to the side band and the transmitter 18 will send out only the other. frequency bands. While I have only shown and de-.

scribed the simple case of intercommunication between only two parties it is to be distinctly understood that my system may be adapted for communication between any number of parties by simply adopting for the system any of the well known selective schemes now employed. It is also within the purview of my invention to allow for the calling of any number of subscribers utilizing a system which is well known in the automatic telephone art, that is, by the use of the well known dialing system and automatic central. it is not necessary in this place to give further details as to how .such selecting process takes place since it is fundamentally well known in the prior art, and since it does not form part of this invention. Sutlice it to mention that the line relay B, C controls and operates the transmitter 18 by convenient contacts (not shown here) so that at the other apparatus stepping switches. (being, for instance, suitably connected with relay A) are set by steps in well-known manner at the rate and rhythm of the incoming ring ing impulses so that, after completion of the latter, the ringing device is released and on; erated at the particular radio frequeneyQsubscriber to which the number of impulses sent out is coordinated. 1

In drder that my invention may be more clearly understood Iwill herein describe the exact function of the relays which form an important part of the system. Thus, considthe subsequent conversation the carrier wave for the excitation of transmitter 18 and for heterodyning in the receiver 19 must be furnished from the generator or oscillator 44: of that particular station, hence, the said generator must then be connected by way ofthe make and break contacts d (i with the leads 32, 32 of the exciter circuit connected to the transmitter 18 and also by way of back contacts d (i to the heterodyne circuit of the receiver. However, when the tratfic with the corresponding or cooperating station is initiated by a call from this corresponding station then the carrier wave is not generated at the station in question but the receiver 19 receives the carrierwave from the corresponding station and from'a suitable point of its radio frequency circuits, this radio frequency energy istderived and fed to the exciting circuit of transmitter 18 by way of the leads 15, 15. Hence for this purpose the contacts d d must be open while the contacts (1 (i must be in their lower position. In addition the filter 35 which must now be impermeable for the carrier wave and filter 25 which must now be permeable for the carrier wave must be reversed so as to bring about this condition, 3y shifting over the, cooperating contactsd The operation and control of all of'these contacts as well as its own holder contact (i is controlled by relay D which upon energization causes a reversal of all of these contacts, namely, d d d d d (Z and (1 Relay A serves for the energizing of the relay D upon an incoming call. Part of the radio frequency energy coming in at the receiver is fed to the apparatus 20 where it is rectified and amplified. The insuring rectified and amplified current energizes relay A which serves to close the contact a whereby the relay magnet D is energized.

The relays B and C may be considered as one relay primarily for the purpose of precluding the use or the actuation of relay D whenever the communication is initiated from the station in question. Thus, when the subscriber lifts the telephone receiver both the relays B and C become energized. It should be here noted that the reason Why therelay was made in two parts, namely, B and C is in order that the battery 6 might be symmetrical to. the supply leads 1, 2. It is to be understood, of course, that the relays B and C could be combined and become a single relay without defeating the operation of switch 6 of the oscillation generator 44 so that in this position the generator 44 can furnish a carrier wave to the transmitter 18 for during the conversation even if the relay A' happens to be accidentally de-energized for a brief period so that contact a becomes deenergized.

It may be mentioned in concluding that if, say due to an inexact differential connection at the audio frequency end undesiredbackfeeds occur between the receiver and the transmitter, these difficulties can be obviated by that, for instance; during transmission the audio frequency output circuit of the receiver is blocked, and during receiving the radio frequency output circuit of the transmitter is blocked.

In what way such blocking may be insured automatically in dependence upon the sending or receiving suflice it to say that when, at the transmitter, as shown in Fig. 2, a differential relay 48 passed by the two plate currents is used, this relay is entirely neutralized during pauses in the conversation, while it is energized during conversation owing to the resultant dissymmetry in the two plate currents; and this energization can be used for the purpose to occasion the desired automatic actuation of the stopper means, for instance, by eliminating the stopper action in the transmitter outlet (output) when talking andto produce blocking action in the receiver output.

I claim:

1. A two way communication system comprising a bridge arrangement having a receiver circuit and a transmitter circuit connected respectively at diagonally opposite points of said bridge, a low frequency circuit and a high frequency circuit connected respectively to theother two diagonally oppo-' site points of said bridge, a source of highcircuit for controlling said variable contacting means.

2. In a two-way communication system a bridge arrangement having a receiver circuit and a transmitter circuit connected respectively to diagonally opposite points of sa1d bridge, a low frequency signalling circuit and a high frequency signalling circuit connected respectivelv to the other two diagonally opposite points of said bridge, a variable frequency suppression device connected in one arm of said bridge, another variable frequency suppression device connected n another arm adjacent to said first mentioned arm and a source of radio frequency current adapted to be connected in a diagonal of said bridge.

3. In a two-way communication system a bridge arrangement having a receiver circuit and a transmitter circuit connected respectively to diagonally opposite points of said bridge, a low frequency signalling circuit and a high frequency signalling circuit connected respectively to the other two diagonal-.

ly opposite points of said bridge, a variable connected respectively to the other two diagonally opposite points of said bridge, a'variable frequency suppression device connected in one arm of said bridge, another variable equency suppression device connected in another arm adjacent to said first mentioned rangement havin transmitter circui t connected re arm, a source of radio frequency current adapted to be connected in a diagonal of said bridge, means in said low frequency signalling circuit for controlling said source and for controlling said variable frequency sup frequency signalling circuitconnected repression devices. a

5. In a communication system a bridge arrangement having transmitter circu1t coupled respectively at diagonally opposite points of said bridge, a low frequency circuit and a high frequency circuit connected respectively to theother two diagonall opposite points, of said bridge, a source of ig frequency current having variable contacting means adapted in one position to connect said source diagonally across said bridge so as to supply energy to both said receiver circuit and said transmitter circuit and in another position to disconnect said source from both said circuits, means in said lowfrequency circuit for controlling said variable contacting means, a variable frequency suppression device connected in an armof said bridge, another variable frequency suppression device connected in another arm adjacent to said first mentioned arm and means in said lowv frequency circuit for controlling said variable frequency suppression devices.

a receiver circuit and a quency circuit connected respectively to the other two diagonally opposite points of said bridge, a source of high frequency current, variable contacting means adapted in one position to connect said source diagonally across said bridge so astosupply ener to both said receiver circuit and said transmitter circuit and in another position to disconnect said source from both said circuits and directly connect said receiver to said transmitter and means in said low frequency circuit for controlling said variable contacting means.

7. In a communication system a bridge ar rangement having a receiver circuit and a transmitter circuit connected respectively to diagonally opposite points of said bridge, an

lntensity regulator operatively associated with said receiver circuit, a low frequency signalling circuit and a high frequency signalling circuit connected respectively to the other two diagonally opposite points of said bridge, a source of radio frequency current adapted to be connected diagonally across said bridge so as to supply said transmitter circuit and receiver circuit with high frequency energy and comprising a relay connected with i 1 said receiver clrcult for rendering sald com- 4 munica tion system operative when a signal is received through said high frequency circuit.

8. In a communication system a bridge. arrangement having 'a receiver circuit and a transmitter circuit connected respectively to diagonally oppositepoints of said bridge, a

low frequency signalling circuit and a high.

spectively to the other two dia-gonall opposite points of said bridgeya source 0 high frequency current having variable contacting means adapted in' one osition to connect said source so as to supp y energy to both said receiver circuit and said transmitter'circuit and in another position to disconnect said means and means connected tosaid receiver circuit for renderin said last named means inoperat ve upon t e receipt of a calling PAUL TATZ."

' signal.

6. In a communication system a bridge ara receiver circuit and a all f d b d at diagon y opposite points 0 S211 ri go a low frequency circuit and a high fi-e- 

